Well logging system



July 25, 1961 E. T. HowEs 2,993,553

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rraRA/Ey United tates ate-nt *l 2,993,553 WELL LOGGING SYSTEM Edgar T.Howes, Pasadena, Calif., assigner to United Geophysical Corporation,Pasadena, Calif., a corporation of California Filed May 9, 1955, Ser.No. '506,819 14 Claims. (Cl. 181.'5)

This invention relates to improvements in systems for logging wells andmore particularly to improvements inV systems for logging the seismicwave characteristics, especially the seismic wave interval velocitycharacteristic, of formations intersected by a well. More specificallythe invention relates particularly to an improved arrangement forgenerating and receiving seismic waves in a well during a loggingoperation. This application is a continuation-in-part of my copendingpatent application Serial No. 462,062, iiled October 13, 1954.

Generally speaking, two types of systems have been developed for loggingthe velocity characteristics of formations penetrated by a Well. Onetype involves the continuous generation of seismic or acoustic waves ofconstant amplitude and frequency at a source and the continuousreception of these waves at Ia receiver. The source and the receiver aremoved along the length of a well together, and either changes inamplitude or phase of the received waves are measured at intervals toprovide an indication of changes in the characteristics of thesurrounding formations as the source and receiver are moved along thelength of the well. A system of this type is described in Cooper patentNo. 2,156,052. In the other type, a seismic wave transmitter is employedto generate a transient seismic wave train, or seismic wave impulse ofshort duration, and such a wave is received at one or more points spacedfrom the transmitter. The transmitter and the receiver, or receivers,are moved together along the length of the well, and the transmitter isperiodically operated to facilitate the measurement of characteristicsof the formation at various depths in the well.

Systems of this type are disclosed in the Wyckoff and Vogel patentsspecifically referred to hereinafter.

Various types of transmitters have been employed as I sources of suchseismic wave impulses. One type of transmitter employs an explosivecharge to generate the seismic impulse. One disadvantage of the use ofsuch an explosive charge to generate the seismic wave impulse resides inthe fact that only a limited number of explosive charges can be carriedin any well surveying device so that it becomes extremely diicult andexpensive to make a continuous survey of a seismic wave characteristicover a great depth range in a well. In other systems, the transmitterhas assumed the form of a iiexible metallic diaphragm arranged in thewall of a source of transmitter, and some sort of means, such as anelectromagnet, is arranged to cause the diaphragm to be displacedsuddenly in order to impart a seismic wave impulse to the iiuid in theWell. No. 2,233,992 which issued to Ralph D. Wyckoff March 4, 1941. Inanother type of transmitter an electric spark has been periodicallygenerated by the discharge of electricity between a pair of electrodesto generate a seismic wave impulse. Such a device is illustrated inPatent No. 2,651,027 which issued to Charles B. Vogel September l, 1953.Electromagnet and spark-type transmitters have not been very eifectivebecause of the fact that it is very difiicult to produce seismic waveimpulses of great strength or high amplitude. For this reason, it isvery diicult to make reliable and accurate logs of seismic wavecharacteristics with them under widely varying conditions such as thosenormally encountered in surveying wells.

In copending patent application Serial No. 462,062

Devices of this type are illustrated in Patent filed by me October 13,1954, thereV is disclosed and claimed a logging system which employs awell unit comprising a seismic wave generator or transmitter and a pairof seismic wave receivers, all arranged within a common housing orcasing, for use in making interval velocity logs. In that application Ihave disclosed a system in which seismic wave impulses are periodicallygenerated at a transmitter and periodically received at the receivers asthe well unit is raised or lowered in the well. An electric triggerpulse is generated each time a seismic wave impulse is generated. Thetrigger pulse is employed in the well unit to switch the output of thetwo receivers so that they are connected to common lines in the cable atthe respective times that the seismic waves are received at therespective receivers. The trigger pulse and the electric waves generatedin the receivers are both transmitted to the surface, where they aredisplayed on a common trace on the face of an oscilloscope together withtiming lines for measuring the time elapsed between the creation of theelectric impulse and the times of reception of the seismic waves at therespective receivers.

The present invention relates particularly to an improved well unit foruse in logging the interval velocity or other seismic wavecharacteristic of a well and which is particularly suited for use in thesystem of copending application Serial No. 462,062.

The invention involves both improvements in seismic wave transmittersand improvements in a combined transmitter and receiver or receivers. Bymeans of the improved transmitter it is possible to generate strongseismic wave impulses. By means of the improvements in the overallcombination it is possible to transmit seismic wave impulses from atransmitter to a receiver or receivers through the formations veryeiectively compared with the transmission by other paths, thusincreasing the accuracy and reliability of the measurements. Y

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method of operationtogether-` with various features and advantages thereof, will be bestunderstood from the following description of a specific embodimentthereof when read in connection with the accompanying drawings in which:

FIGURE l is a vertical cross-sectional view of th earth showing a wellbeing surveyed with the well testing unit of this invention;

FIG. 2 is a schematic diagram of the well testing equipment;

FIGS. 3a, 3b, 3c, 3d, and 3e represent successive segments of the upperpart of the Well testing unit;

FIG. `3 is a diagram showing how the drawings of FIGS. 3a, 3b, 3c, 3d,and 3e are assembled to illustrate the upper part of the well testingunit;

FIGS. 4b and 4c are sectional views taken on the lines 4b--4b and 4c-4cof FIGS. 3b and 3c respectively, of certain segments of the well testingunit;

FIG. 4 is a diagram showing how FIGS. 4b and 4c are assembled to form aportion of the upper part of the well testing unit;

FIG. 5 is a horizontal cross-sectional view taken on the line 5-5 ofFIG. 4b;

FIG. 6 -is a cross-sectional view taken on the line 6-6 of FIG. 4b;

FIG. 7 is a fragmentary perspective view of the chain backing member;

FIG. 8 isa cross-sectional view taken on the line 8'8 of FIG. 3b;

FIG. 94 is a perspective View of a hammer cooking member;

FIG. l0 is a fragmentary perspective view of the hammer hook;

FIG. 11 is a side elevational view taken on the line 11-11 of FIG. 4c;

FIG. 12 is a fragmentary perspective view of the switch;

FIG. 13 is a cross-sectional view taken on the line 13--13 of FIG. 3d;and

FIG. 14 is a graph of a seismic wave impulse of the type generated bythe transmitter.

In the form of the invention illustrated in FIGS. 1 and 2, an elongatedwell testing unit 100 supported by a cable is raised and lowered in awell 20 by means of a winch 22 carried by a truck 24 at the surfacel 25of the earth. The well unit 100 includes a cable connector 101, aseismic wave generator or transmitter 102, a first spacer 103, a rst oran upper seismic wave receiver 104, a second spacer 105, and a second orlower seismic wave receiver 106, all arranged in the order named fromtop to bottom. The well unit 100 is attached tothe lowermost end of thecable 10 by means of the coupler 101. The unit is arranged in anelongated housing which in practice is composed of a series of housingmembers or sections which house separate parts of the Well unit.

A` first or upper flexible coupling device 110 is arranged between thetransmitter 102 and the rst spacer 103, a second or intermediateflexible coupling device 112 is arranged between the rst spacer 103 andthe upper receiver 104 and a third or lower ilexible coupling device1114 is arranged between the upper and lower receivers 104 and 106. Thetransmitter 102, the spacers 103 and 10S, the two hydrophones 104 and106, and the coupling devices 110, 112, and 114 are arranged coaxiallyalong an axis x-x, such as a vertical line, in the order named, with thetransmitter above the hydrophones and with the upper hydrophone 104located midway between the transmitter 102 and the lower hydrophone 106.As will become apparent hereinafter, the coupling devices 110, 11,2 and114 act as vibration filters to attenuate and delay direct transmissionof energy from the transmitter 102 to either receiver 104 or 106 or fromone receiver to the other. At the same time though the upper couplingdevice 110 closely couples the transmitter with liquid such as oil ormud in the Well so as to facilitate transmission of seismic energythrough the surrounding formations to the receivers.

The seismic wave transmitter 102 includes special means for periodicallyradiating a seismic wave impulse into the liquid in which the well unitis immersed and into the surrounding formations 14 through which thewell extends, as described more fully hereinafter. The two seismic wavereceivers 104 and 106 are in the form of hydrophones which respond towaves which travel thereto either directly by a path through the iiuidwithin the well from the seismic wave transmitter 102or indirectlythereto after being transmitted through the formations forming the wallsof the Well 20. Inasmuch as the velocity of transmission of soundthrough the formations is almost invariably greater than the velocity oftransmission of sound through the well liquid, by spacing thetransmitter and the receivers far enough apart, waves transmitted fromthe transmitter through the formations arrive at the receivers beforethe waves transmitted through the liquid and the latter waves do notinterfere with the detection of the arrival of the former. However,unless precautions are taken in accordance with this invention,vibrations transmitted through the housing might arrive at a receiverbefore the waves travelling through the formations and interfere withthe detection of the iirst arrivals of the latter at the receiver.

In the system described specifically in my copending patent applicationSerial No. 462,062, the well unit 100 also includes certain subsurfaceelectrical equipment 'El and certain surface electrical equipment E2that is located at the surface and is connected thereto through thecable 10 as shown in FIG. 2. This equipment is employed' fortransmitting to the surfacel unit a time break Signal TB that indicatesthe instant of operation of the transmitter and other signals FB1 andFB2 that correspond to the first breaks of seismic waves that arereceived by the hydrophones 104 and 106 and that indicate the instantsof arrival of waves at the hydrophones 102 and 104. The electrical unitsE1 and E2 operate to display the time break TB and first breaks FE1 andFB2 on a single trace of an oscilloscope O, the three first breakscorresponding to the instants at which the trigger pulse is generatedand the instants at which seismic wave pulses are first received at thereceivers 104 and 106. This record also displays a plurality of verticaltiming lines T -to facilitate measurement of the time of travel ofseismic Waves from the transmitter 102 to each of the receivers 104 and106. The details of the subsurface electrical equipment E1 and thesurface electrical equipment E2 which are employed to produce a seriesof such records at various depths in a well are described in saidcopending patent application Serial No. 462,062.

As illustrated very schematically in FIG. 2, the seismic wave source, ortransmitter, 102 of this invention comprises a hammer 120 which isnormally urged toward the downward or lowermost position by means of astrong extension spring 122. A D.C. electric motor 124 driven byelectric power supplied from the surface through the cable 10 isemployed to slowly raise the hammer 120 periodically to its uppermostposition and to release it periodically to cause the hammer 120 tostrike an anvil 126 that is disposed directly beneath the hammer 120 andis rigidly secured to the housing member ofthe transmitter 102.

The mechanism for raising and releasing the hammer 12,0 includes a chain130 that passes over a driving sprocket 128 and over a driven sprocket132. The driving sprocket 128 is driven by the motor 124 through a geartrain 162V. The chain 130 carries a pair of outwardly projecting cockingmembers in the form of fingers 134 which are located at equally spacedpositions on thc chain. As each of the fingers 134 passes upwardlyadjacent the hammer 120, it engages a hook 248 on the hammer therebyforcing the hammer upwardly against the force of the spring 122 andstoring potential energy in the spring 122 and in the hammer 120. Wheneach of the fingers 134 reaches its uppermost position and withdrawsfrom the hammer 120, it becomes disengaged from the hook 248 therebyreleasing the hammer and permitting the spring to force the hammer 120downward rapidly to strike the anvil 126. The motor 124 is drivencontinuously, thereby causing the hammer to strike the anvil 126periodically at regular short intervals of time such as once every fiveseconds. Each time the hammer 120 strikes the anvil 126 it also closes anormally open switch 131 to generate a trigger pulse which is employedto operate the subsurface electrical equipment El and the surfaceelectrical equipment E2, as described more fully in my copending patentapplication Serial No. 462,062.

As the cable 10 is raised or lowered in the well, the well unit passesthrough various formations which are characterized' by different seismicwave velocities. Each time the hammer strikes the anvil 126 a seismicWave impulse is transmitted outwardly from the seismic wave generatorand into the surrounding formations through which they ltravel to theseismic wave receivers 104 and 106. Seismic wave energy which hastraveled through thev adjacent formation reenters the well, arriving atthe hydrophones 104 and 106 at spaced time intervals. By recording thetime break TB and the first breaks FBIy and FB2 each time a seismic waveis generated, a record such as that shown in Fig. 2 is produced. By.measuring the depth at which the well unit is located at the time thateach record is produced as the cable is moved along the length of theborehole, a seismic wave interval velocity log is obtained.

antrag-a The well unitY 100, and more particuiarly the seismic wavetransmitter 102, will now be described in some detail generallyfollowing a sequence from top to bottom. In this connection it is to benoted that the details of a complete seismic wave transmitter 102,together with certain associated parts, are illustrated in FIGS. 3a, 3b,3c, 3d, and 3e, and in part in FIGS. 4b and 4c. The seismic wavetransmitter 102 comprises a tubular housing member 140 which isconnected at its upper end to the cable connector 101 as shown in FIG.3a and at its lower end to the upper coupling 110 as shown in FIG. 3d.The anvil 126 is arranged as shown in FIG. 3d at the junction betweenthe transmitter 102 and the upper coupling device 110. Suitable meansare employed for leading conductors, designated only in a general way bythe symbol C, from the cable through the cable connector 1011 into thehousing section 140 and through the anvil 126, the coupling device 110,the receiver 104, the coupling device 112, and to the lower receiver 106as needed. In any event, the housing member 140 of the transmitter 102is filled with air or some inert gas and is sealed by suitable means torender it fluid-tight to prevent leakage of well uid into thetransmitter even at the high pressures encountered at depths of 10,000feet or more in a deep well. But the coupling device 110, which is alsoof hollow tubular configuration, is lled with oil or some other suitableliquid and is sealed to render it fluid-tight to prevent leakage of wellvfluid into it when in a well and to prevent leakage of air into it whenthe well unit is exposed to the atmosphere at the surface and generallyto prevent leakage of the oilA or other vliquid from the coupling deviceat all times.

A billet 142 locked by means of a lock nut 144 and sealed by an O-ring146 is rigidly secured to the upper end of the housing member 140,sealing it against leakage of air or ingress of liquid. 'I'he billet 142is provided with a plurality of longitudinal passages 148 through whichvarious conductor sections 149 extend, these conductor sections beingsealed in place in some suitable fashion to render the passages 148duid-tight. A cylindrical container 150 which encloses the subsurfaceelectrical unit E1 is securely fastened to the lower end of the billet142 by some suitable means such as screws 152. A screw 153 at the top ofbillet 142 facilitates its insertion and removal. A spacer sleeve 154 issecurely fastened to the lower end of the billet 142 by means 0f abayonet lock 156 and a set-screw 158. The spacer sleeve 154 is designedto fit closely between the case 150 and the housing member 140.

As shown in FIGS. 3b and 4b, the motor 124 is located at the bottom endof the spacer sleeve 154. Certain conductors C that are connected withthe cable 10 are employed to supply D C. current to the motor 124. Slots158 formed in the lower end of the spacer sleeve 154 facilitate thepassage of other conductors C downwardly past the motor 124 to pointswhere connections thereto are needed in the well unit.

As shown in detail in FIGS. 3b and 4b, the drive shaft 160 of the motor124 drives the driving sprocket 128 through a speedreducing gear train162. The input shaft 164 of the gear train is connected through asuitable coupliug 165 to the motor drive shaft 160, the input shaft 164and the motor shaft being coaxially and longitudinally mounted withinthe housing member 140. A driving bevel gear 166 at the lower end of theinput shaft 164 engages a driven bevel gear 168 mounted on a firsthorizontal or transverse shaft 169. A small spur gear 170 mounted at thecenter of the shaft 169 drives a large gear 171 on a second horizontalor transverse shaft 172. A spur gear 173y on the shaft 172 engages alarge gear 174 on a third horizontal or transverse shaft 175. Likewise,a small spur gear 176 on the shaft 175 engages a large gear 177 on afourth transverse or horizontal shaft 178. Similarly, a spur gear 179 onthe shaft 178 engages a large driven gear 180 at the center of a .6fifth transverse or horizontal shaft 181. Spur gears.182 at the oppositeends of the shaft 181 engage large .idler gears 184 arranged on oppositeends of a sixth horizontal or transverse shaft 183, the idler gears inturnengaging driven gears 185 at opposite ends of a seventh horizontalshaft 186 which carries the driving sprocket 128. All of the horizontalshafts are arranged in suitable ball bearings mounted within acylindrical housing 190, the shafts being arranged one beneath the otherin the order named in a common central longitudinal plane.

As shown in FIG. 5, the housing 190 is split, being formed of two verysimilar semi-cylindrical parts which are rigidly secured together bybolts 192 (see FIG. 3b) and aligned by means of mating flanges 194.Channels 196 formed in the outer surface of the gear housing 190 areemployed to permit the passage of electrical conductors C past the gearhousing.

It will be noted that as power passes through the gear train, the speedis reduced as movement is imparted from one shaft to anothersuccessively. However, as the speed of rotation of the shafts decreasesfrom shaft to shaft, the torque applied to the gears increases. Byemploying gears at both ends of the lower shafts 181 and 186 strain onthe individual gear teeth on these shafts is reduced. One of the idlergears 184 is keyed to the shaft 183, while the other is permitted torotate freely thereon so as to minimize any danger of misfit orexcessive Wear between the upper pair of gears 182 and the lower pair ofgears 185 which engage the idler gears.

The driven sprocket 132 is mounted, as shown more particularly in FIGS.4c and 1'1, on a bearing support 200 which may be adjusted in positionlongitudinally within the housing 140 by means of adjusting screws 202which engage the lower end of a guide block 204'which in turn engagesthe lower end of the gear housing 190. After adjustment, the bearingsupport is locked in place by means of screws 305. l

As shown more particularly in FIG. 6, the guide bloc 264 is split, beingdivided into two similar sections in which facing grooves 206 form arectangular passage 205 extending from one end of the guide block 204 tothe other. The two sections of the guide block 204 are rigidly securedtogether by means of mating anges 209 and suitable bolts 208. The guideblock is also provided with external passages 210 to permit the passageof conductors C. The rectangular passage 205 is sufficiently large topermit the chain to move freely therein when driven by the drivingsprocket 128. The guide block 204 serves not only to support the chain130` but also to guide the hammer in its up and down path as more fullydescribed below. The guide block 204 thus acts as an upper hammer guide.

The chain 130 consists of a series of conventional links 212 connectedby pins 214 for engaging the sprockets 128 and 132. However, two of thelinks 216, illustrated in detail in FIG. 9, are provided with taperedfingers or extensions having broad abutments 2:20 at the leading edgesthereof. The two extended links 216 are located half a chain lengthapart and are used as cocking members or fingers for raising andreleasing the hammer 120 as described more fully hereinbelow.

An intermediate hammer guide 221 in the form of a tubular member orcylinder is fastened by means of screws 222 to the lower end of theupper hammer guide 204. The lower end of the intermediate guidef221 iscentered in the housing member by means of a lower hammer guide 223which is in the form of a tubular member or cylinder of smaller`diameter which extends into the cylinder 221. The upper end of thetubular member 223 is spaced from the tubular member 221 forming anannular space 224 between the intermediate and lower hammer guidemembers 221 and 223. A

spacer 225 that threadably engages the lower end of the lower hammerguide 223 engages the lower end of the intermediate guide 221 and it isseated at its lower end against the upper surface of the anvil 126. Theoutside diametrff the ylladerv 221 is smaller than the inside. diameterof-A the housing member 140, thereby providing an annular space 227through which various conductors may pass, ther lower ends of theconductors extending through inclined passages 228 at the upper end ofthe spacer 225. The conductors tit only loosely in the passages 297thereby permitting air to flow freely therethrough when the hammer israised and lowered.

The hammer 120 itself is of unitary construction, being provided with aheavy elongated cylindrical body or core 230 at its lower end and arelatively light rectangular arm 232 extending upwardly from its upperend. An outwardly extending flange 234 between the body 230 and the arm232 slidably engages the inner surface of the intermediate hammer guide221, while the foot 236, at the lower end of the body 230 slidablyengages the inner surface of the lower hammer guide 223. Holes in thelower end of the intermediate hammer guide 221 permit the free ilow ofair therethrough during the operation of the hammer.

The hammer arm 232 is milled out to form a U-shaped member comprisingtwo straight parallel legs 240 connected together by means of datwebbing 242. A pair of outwardly extending ears or rails 244 are formedat the upper end of the arm 232. An opening or window 246 cut in theupper end of the webbing 242 terminates in a bridge 247 thus forming ahammer hook 248. To increase the strength and durability of the hammerarm in operation, all surfaces of the hammer arm 232 are finished to asmoothness of at least about 16u inch R.M.S. and the surface is renderedsubstantially free from irregularities that would be visible to theaverage eye at a distance of about 18 inches. The irregularities thusremoved include scratches, pit holes, or other indentations and alsolarge or sharp protrusions. Furthermore, to increase the strength of thehammer arm 232, the upper corners of the window 246 are notched asindicated at 250 in FIG. r8, and the various edges of the hammer arm,especially those at the edges of the window are rounded to eliminatesharp edges. The radius of curvature of the rounded portions should beat least about 0.01 inch.

The hammer arm 232 extends upwardly along one side o f the rectangularwindow 207 of the upper hammer guide 204. As indicated in FIG. 6, thelegs 240 of the hammer arm 232 slidably engage the side walls or" thepassage 205 and the ears o r rails 244 slidably engageV grooves 252 atthe corners of the passage 205` A support mem.- ber 254 of L-shape, asindicated in FIGS. 6 and 7 as well as in FIGS. 3b and 3c, provides abacking platte 260 to assist in preventing excessive inward flexure ofthe chain 130 during operation -while it is raising the hammer 120,thereby preventing the hammer hook 248 from slipping inadvertently fromthe fiinger 218 during operation.

An electric switch 270 is mounted at the upper end of the anvil 126where it may be operated each time the hammer 120 is released to strikethe anvil. As shown in more detail in FIG. l2, the switch 270 comprisesa stationary electrical contact 271 mounted on a block 273 of insulationmaterial and a pair of resilient movable contacts 274 on opposite sidesthereof. The stationary contact 271 is connected to one conductor 275and the pair of movable contacts are connected to another conductor 276.The two resilient movable contacts 274 are normally held apart invspaced relationship from the stationary contact 271 by an insulating arm277 which is arranged to rotate about a horizontal `axis established bya p in 2 78. A torsion spring 279 normally pivots the insulating arm 277to a horizontal position where an outwardly extending nger 280 restsupon the stationary contact 270 and holds the movable contacts 274 intheir open circuit position spaced from the stationary contact 2 71. Aninwardly extending nger 282 of the arm 277 projects across the path oflthe hammer body 230 so that whenwthe hammer is lowered, it pushes theinwardly extending linger 2.82 downwardly;4 Biting they outwardlyextending iinger 2 80 oftthe stationary contact 271 permita ting theresilient movable contacts 274 to contact the sta@ tionary contact 2711,thereby closing a circuit to create a trigger pulse for use in theoperation of the. subsurface and the surface electrical units E1 and E2.

A cylindrical insulation ring 283, on which the switch 270 is mounted,is provided with suitable connectors 284 for joining parts of theelectrical conductors C that pass through the anvil 126. Passages 297extending longitudinally through the anvil are provided to permit theleading of conductors through the anvil 126 to the receivers 104 and106. An upwardly projecting head 286 of the anvil 126 extends upwardlythrough the ring 284 and terminates just beneath the switch operatingarm 277 as indicated in FIG. 13, so that when the hammer approaches theanvil the trigger pulse created by the closure of the Switch 146 isproduced simultaneously with the initial impact of the hammer on theanvil.

A helical spring 292` encircles the hammer body 230. The upper end ofthe helicalA spring is anchored by a rivet or pin 293 to the upper endof the hammer body 230 directly beneath the flange 234, and the otherend of the spring is attached to the outer end of the lower hammer guide223. The turns of the helical spring 292 between the ends thereof arenormally spaced apart. However, a few turns at the upper end and a fewat the lower end are closely spaced and are arranged to engage helicalgrooves 295 in the hammer body and grooves 296 inthe lower hammer guide223.

The coupling device is an improvement in the type described and claimedin my copending patent application Serial No. 366,271, now Patent No.2,788,510. The coupling device 1,10 comprises upper and lower tubularconnectors 300 and 302 and an interconnecting resilient member 304. Theupper tubular connector 300 threadably engages the lower end of theanvil 126. The lower tubular connector 302 threadably engages aconnector 306 which facilitates connection of the transmitter i102 tothe spacer 103.

The interconnecting resilient member 304 comprises a helical spring 310which is threaded onto the lower end of the upper tubular connector 300and onto the upper end of `the lower tubular connector 302, being lockedthereon by bodies of rubber which are cured in place on the threadedparts of the spring. The resilient member 304 also includes a protectiveelastic sleeve 312 composed of rubber or other suitable material whichencloses the spring 310. The rubber sleeve 312 is clamped in place aboutthe threaded ends of the spring 310 by means of straps 311 and 313.

The upper end of a stretch limit member 314 is connected by a bolt 316to the anvil member 126. The lower end of the stretch limit member 314is connected by a bolt 318 to a piston 320 which is slidably mountedwithin the lower tubular connector 302. A rubber ring 321 bonded ontothe outer rim of the piston 320 prevents metal-to-metal contact betweenthe piston and the lower tubular connector 302. A shoulder 322 formed inthe lower tubular connector 302 limits the upward movement of the piston320 therein, thereby limiting the extension or stretching of theresilient member 304 including the spring 310 and the elastic sleeve312. Holes 323 formed in the piston 320 facilitate the leading ofconductors downwardly to the receivers 102 and 104.

The lower tubular connector 302 includes a threadably removable section303 which is threaded directly into a connector 306 at the top of theupper spacer '103. The connector section 303 is provided to facilitatethe assembly of the tool and is provided with a bayonet connection 324to permit locking an electrical connector 326 at its bottom end.

The entire space between the anvil 126 and the electrical connector 3'26is sealed to prevent ingress or egress of fluid therefrom, and thisspaceis filled with ol through escasas filler ports 328 extendinglaterally into the anvil 126 from opposite sides thereof andcommunicating with longitudinally extending passages 329 which lead intothe interior of the cupling device 110. In practice the coupling device110 is filled with oil while the coupling device is extended under loadand care is exercised to eliminate air bubbles from the interior of thecoupling device 110.

The coupling devices 112 and 114 are of substantially the sameconstruction as the coupling device 1'10 which has been described indetail in connection with Figs. 3d and 3e.

Each of the spacers 103 and 105 comprises a tubular housing member whichis connected in any suitable manner between the transmitter 102 and thereceivers 104 and 106. c Each of the receivers 104 and 106 is in theform of a hydrophone of the type described and claimed in copendingpatent application Serial No. 366,093 led by Douglas G. Marlow July 6,1953. The hydrophone 106 comprises a pressureresponsive element 330-which is in direct communication with fluid in a lateral passage 332extending through the housing member of the hydrophone near the upperend thereof as indicated in Fig. 2. The pressure-responsive element maybe in the form of a piezoelectric crystal which is connected to theinput of a preamplier 334. The lower receiver 106 is of a constructionsimilar to that of the upper receiver 104, being provided with apressure-responsive element 340 adjacent a lateral passage 342 at itsupper end, and a pre-amplifier 344 connected to the element 340.

Conductors in the outputs of the pre-amplifiers 334 and 344 leadupwardly through the various sections of the testing unit to thesubsurface electrical unit E1. Thus suitable output conductors leadupwardly from the lower pre-amplifier 344 through the coupling device1'14 and through the spacer 105 into the receiver 104. From there theseconductors and also conductors connected to the output of the upperpre-amplifier 334 lead upwardly through the coupling device 112 and thespacer 103 into the transmitter 102 where they feed signals into thesubsurface electrical unit El. Here a signal produced by the closing ofswitch 270 operates to cause signals from the outputs of the twopre-ampliiiers to be transmitted through the cable to the surface of theearth. Other conductors as needed are led through the various sectionsof the testing unit 100 to the cable 10.

Details of the spacers and the hydrophones and the electricalconnections are not disclosed herein, since no claim to such details perse is made herein and since spacers and hydrophones and electricalconnections may be embodied 4in many forms within the scope of thepresent invention.

To make an interval velocity log of a well, the testing unit 100 islowered into the well by paying out the cable 10 from the winch '22.Subsequently the testing tool is raised in the well by winding up thecable `10 onto the winch 22. Either while the testing unit 100 is beinglowered into the well or while it is being raised upwardly therein,power supplied from a battery or generator in the truck 24 is fedthrough the cable 10 to the motor 124 causing the motor to rotatecontinuously, thereby driving the endless chain 130 continuously. As thechain 130 is continuously moved over the sprockets 128 and 132, theextended links 216 thereon periodically engage the hook 248 of thehammer, raising the hammer against the force exerted by the helicalspring 262 and extending the helical spring, thereby storing potentialenergy in the spring. At the top of the hammer stroke the link becomesdisengaged from the hook, thereby releasing the hammer.

'Ihe hammer arm 240 is so arranged that the hook 248 lies adjacent thelower sprocket 132 whenever the hammer 120 is in its lowermost positionin which the hammer engages the anvil 126. Each time one of the extendedlinks 216 passes near and beyond the lower sprocket v4132 it engages thehook 248, thereby raising the hammer 120 upwardly, drawing it away fromthe anvil 126. As the hammer 120 is raised, the spring 262 s extended,thereby storing potential energy therein. As the extended link 216 thatis in engagement with the hook 248 approaches and passes near the uppersprocket 128, the hook 248 is released. Upon release, the spring 262forces the hammer downwardly, causing it to strike the anvil 126 at arelatively high speed.

In a specific embodiment of the invention employing a spring 262 havinga compliance of about 20.1 lbs/in. and a hammer weighing about 3.5 lbs.,`when the amplitude of the hammer stroke was 0.5 ft., the hammer 120struck the anvil 126 at a velocity of about 18'/ sec. The anvil itself,in this specific embodiment of the inventionl weighed about 7.5 lbs.,and it was rigidly secured to the: lower end of a transmitter unit 102having a total weight of about lbs. 6150 steel. The length of the hammerbody was 14 and the length of the hammer arm was 15". The diam eter ofthe hammer body and the head of the anvil were the same, being about 1.The overall length of the anvil was about 51/2" and the diameter of themain body of the anvil was about 31/2". In practice, when using a 1/12H.P. D.C. electric motor to drive the chain 130 through a speed reducinggear of about 700 to l ratio, the hammer strikes the anvil periodicallyat intervals of about 5 seconds. At the same time that each seismicimpulse is generated, an electric trigger pulse is created by theclosing of the switch 270, and this trigger pulse is employed to operatethe subsurface electrical circuit E1 and the surface electrical circuitEZ as previously mentioned.

Each time the hammer 120 is released, it strikes the anvil 126 causing asharp seismic or acoustic impulse of short duration to be applied by theanvil 126 to the liquid in the borehole and to the neighboringformations. Though the impulse may be of widely different forms andstill be effective for logging a well, it is believed that close to theanvil the seismic wave emitted is of the general shape indicated in thegraph of FIG. 14. Here it will be noted that the impulse has a verysteep wave front F at its beginning and that this wave front is followedby a series of lobes L1, L2, etc., each of short duration and forming aseismic wave train. The duration of each of the first lobes L1, L2, etc.is very short, being of the order of less than 0.0001 sec., though laterlobes (not shown) may be longer duration. Such a seismic wave impulsehaving a steep wave front F and narrow rst lobes is characterized by abroad high frequency spectrum, being rich in frequency components over awide range from below about 1000 c.p.s. to above about 50,000 c.p.s. Thepresence of such high frequency components facilitates the accuratetiming of first breaks to about 0.00001 sec.

The anvil 12,6, being thick, along its axis acts as a thick solid plateor short rod rather than as a vibratory diaphragm. For this reason thefrequency characteristic of the first lobe of the impulse does notdepend on the bending characteristics of the anvil as is the case with adiaphragm, but upon the velocity of transmission therethrough and thelength of the anvil. Furthermore, the anvil does not vibrate like adiaphragm each time it is struck. A compression wave imparted to theupper surface of the anvil travels therethrough with the speed of soundto the lower surface of the anvil. The lower surface of the anvil 126 isclosely coupled to the liquid in the well and to the neighboringformation of the earth by virtue of the design of the coupling device110. The close coupling between the anvil 126 and the liquid in the wellis brought about by virtue of the lfact that the lower surface of theanvil is in direct contact with the liquid contained within the couplingdevice and by The hammer and anvil were made of' virtue of the fact thattheV sleeve 312, of the coupling device is thin and elastic, and byvirtue ofthe fact that the liquid on opposite sides of the sleeve hasvery nearr the same acoustic irnpedances usually differing by no morethan a factor of 2 so that very little impedance is offered to thetransfer of seismic or acoustic energy from the liquid in the couplingdevice to the liquid in the well outside the coupling device. For thisreason a large amount of the energy transmitted by the hammer to theanvil is radiated as an impulse of short duration into the surroundingwell liquid.

It is to be noted that when and only when the anvil is coupled to theliquid or to the formations is energy transmitted into the formations.In the specific embodiment of the invention described herein, closecoupling and hence high efficiency in imparting energy to the formationare achieved by virtue of the fact that the anvil is in contact with oilin the coupling device and this oil in effect is separated from the wellfluid by a sleeve which is substantially acoustically transparent. Itwill be understood, however, that close coupling could be attained byremoving the sleeve and permitting the well fluid to contact the anvildirectly.

The seismic impulse that is thus transmitted to the liquid in theborehole enters the neighboring formations where some of the seismicimpulse energy travels downwardly through the formations along the wallof the borehole to the pressure-responsive elements of the receivers 104and 106. Electrical waves generated by the pressure-sensitive elementsof the receivers are amplified in the receivers and transmitted to thesurface, where their times of arrival are measured relative to theinstant at which the seismic impulse is generated in the transmitter102, all as more fully described in said copending patent applicationSerial No. 462,062. The relative times of arrival of a seismic impulseat the receivers is employed to determine the velocity of transmissionin the neighboring formation. By obtaining such measurements at a seriesof depths in a well, an interval log of the interval velocity of thewell as a function of depth is obtained.

When the hammer strikes the anvil it bounces from it slightly and thenstrikes it again at intervals of about 1/1 sec. Even when the distancebetween the hammer and the lower receiver 106 is as great as about 20`ft. and even more, the second impact does not occur until after thewaves travelling through the formation have arrived at the lowerreceiver 106. Thus later impacts donot interfere with the desiredobservations. The use of such large distances becomes practical with theefiicient source of this invention.

The coupling device 110 serves not only to couple the anvil 126 with theliquid in the well and with the surrounding formations, but it alsoserves to decouple the housing member in which the transmitter 102 isarranged from the other sections of the testing unit. The couplingdevice 112 decouples the spacer from the two receivers 104 and 106. In asimilar way the coupling device 114 that is located between the tworeceivers 104 and 106 decouples the housing members in which the tworeceivers are mounted.

The housings of the transmitter 102, the receivers 104 and 106 and thespacers 103 and 105 are composed of steel or some other suitably strongand rigid material.` Metals and other materials of that type arechanacterized by high sound velocities of the order of 15,000/ sec. Theseismic wave velocities characterizing the formations that intersect thewell vary over a wide range from about say 5,000/sec. to about20,000/sec. For this reason, any vibrations imparted by the anvil to thehousing of, the transmitter would tend to` travel rapidly tothe housingof the spacer 103 and from it to the next adjacent receiver 104, and anyvibrations entering the housing of the spacer 103, or housing of theupper receiver 104 or the spacer 10S, wouldtendto travel. to thelowerreceiver 106,- unless precautionsy are taken to prevent suchtransmission vof vibrations. The arrival of such vibrations at thereceivers would tend to interfere with or conceal the vibrationsreachingthe pressure-responsive elements of the receiver through thesurrounding formations. For this reason the coupling devices 110 and 112are in the form of vibration filters which attenuate and retard thetransmission of vibrations from one housing member to another.

The velocity of transmission of vibrations through each coupling deviceis low, partly because of the fact that the metallic spring 310 is ofhelical configuration, thereby establishing a long path for thevibrations to travel at high speed from one housing member to another,and also by virtue of the fact that the velocity of sound through thesleeve 312 is low. Furthermore, the sleeve 312 itself, being in contactwith the helical spring 310 which it encloses, tends to damp orattenuate any vibrations, particularly exural vibrations, which aretransmitted along the helical spring. Furthermore, even though theextension member 314 is composed of metal characterized by a high soundvelocity, any vibrations that are transmitted along the extension member314 are insulated from the housing member beneath it by virtue of theslidable mounting of the cylinder 320 in the lower connector 302 of thecoupling `device and also by virtue of the insulating effect of therubber ring 321 on the periphery of the cylinder 320.

Furthermore, the coupling devices 110, 112 and 114 act as complianceelements that cooperate with the inertias of the spacers 103 and 105 andthe inertias of the receivers. 104 and 106 to lformt low-pass vibrationfilters, thereby highly attenuating the transmission of any highfrequency components of Waves downwardly along the length of the testingunit 100. The low-pass mechanical or vibration filter so formed has acut-off frequency of between about l c.p.s. and about c.p.s. As aresult, over a range at least, this filter attenuates components athigher frequencies by larger and larger amounts as the frequencyincreases. This range extendsv to a point above the cut-off frequency ofthe high-pass characteristic of the receiver.

The pre-amplifiers 334 and 344 connected with the.

pressure-responsive elements themselves have high-pass characteristics,having a rlow frequency cut-off between about 400 c.p.s. and 1000 c.p.s.Since the particular pressure-responsive element responds uniformly overa wide frequency range, the receiver as a whole has ia high frequencycharacteristic. In a particular case the cut-olf frequency of thischaracteristic was set at about 600 c.p.s. At this frequency theresponse was only about of the response at higher frequencies of about2000 c.p.s. and higher. Below the low `frequency cut-olf limit the4receiver attenuates at a rate of about 6 db./octave the low frequencycomponents of waves thatmight otherwise be transmitted by thepressure-responsive elements to the surface, the attenuation increasingat a rate of 6 db./octave below about 600 c.p.s.

Thus the coupling devices act as vibration filter units which act aloneto a certain extent to attenuate and retard the transmission ofvibrations from one housing memberV of the testing unit to another overa wide range of the spectrum from Ivery low frequencies of, say, c.p.s.to-

very high frequencies of, say, 50,000 c.p.s. and more. At the same timethey also cooperate with the inertias of various sections of the testingunit and with the. preamplifiers to attenuate the transmission ofcomponents of relatively low frequency below about 600 c.p.s. present invibrations. detected by the pressure-responsive unit.

The compliance and inertia characteristics of the low pass filtersformed by the coupling devices 110, 112, and 114 and the various inertiamembers are established very 13 largely by the following specificfactors or characteristics of the elements of the testing unit:

Total mass above upper coupling device 110 -..pounds.. 100 Total massbelow upper coupling device 110 1-.. do 300 Total mass belowintermediate coupling device 112 do 210 Total mass below lower couplingdevice 114 do 70 Stretch of upper coupling device 110 Without rubbersleeve incheL- 3 Stretch of upper coupling device 110 with rubber sleevedo 5%@ Stretch of intermediate coupling device 112 Without rubber sleevedo- 2% Stretch of intermediate coupling device 112 with rubber sleeve do1%@ Stretch of lower coupling device 114 without rubber sleeve do- 31AStretch of lower coupling device 114 with rubber sleeve do 7A;

While-the transmission characteristics of the low pass mechanical filterestablished by the values' of the compliance of the couplers and thevalues of the masses given approximately above, are not determined bythese values alone, but also by other factors including among others thelengths of the elements and the density of the iiuid in which they aresuspended yand the diameter of the borehole in which the testing unit issuspended, nevertheless they do provide an index of the transmissioncharacteristics of the low-pass iilter formed by them at low frequenciesWhere the compliance values and inertias may be lumped. In an)r event,the cut-off frequency 'of the low-pass filter so formed when the testingunit is actually in use should be very low and in any event no more thanabout 1,450 to about 1A() of the cut-off frequency at the low frequencyend of the high-pass characteristic of the receivers. Thus the cut-offfrequency of the lowpass lter so formed is made less than about 50c.p.s.

` It must be borne in mind that the action of the vibration, ormechanical, lilter so provided, when considering the compliancecharacteristics of the couplers' as lumped elements, is quite diiferentfrom the action of the couplers when considered merely as transmissionlines along which energy, especially high frequency components thereof,is transmitted from one part of the testing unit to another'. Theeiectiveness of the coupling device in the latter respect is determinednot merely by the combined action of the coupler compliances and themasses of the associated elements, but also by the action of thecouplers in transmitting sound therethrough along their length. Whentransmitting sound in this manner, the coupling device 110 attenuatesthe transmission of energy from the transmitter 102 to any of the partsbelow including the spacer 103 and the receivers 104 and 106 verylargely by virtue of the fact that the cross-sectional area of thespring wire and the cross-sectional area of the rubber sleeve are verysmall compared with the cross-sectional area of the anvil. Furthermore,the transmission of energy from the transmitter to parts below it isretarded very largely because of the fact that the spring interferes '14the spring is low, the longitudinal speed of sound through the spring isgiven by the formula where:

N=number of turns per inch R=radius of helix V=velocity of sound in themetal forming the spring Vx=speed of travel of sound in the direction ofthe longitudinal axis X--X In a specific embodiment of the invention,the number of turns per inch was approximately 2 and the radius wasabout 2, so that the longitudinal velocity was about 3,000 ft./sec., aspeed substantially below the speed of sound in water even though thevelocity of sound in the spring metal was about 15,000 ft./sec. In anyevent, the longitudinal velocity of sound along the length of thecoupler is made less than the lowest seismic wave velocity to bedetected, and in any event is preferably less than about 5,000 ft./sec.,which is approximately the speed of sound in the liquid filling thewell.

From the foregoing description, it is apparent that a well testing unithas been provided with an efcient transmitter and with effectiveinsulation means for pre venting direct transmission of interferingsignals from the transmitter to a receiver through the well testing unitand thence to the surface both at low frequencies and at highfrequencies.

Though the invention has been described with particu- Ilar reference tothe logging of the interval velocity of formations intercepted by awell, it may also be employed to log other seismic wave charactertisticsof the formations. For example, by periodically generating a seismicimpulse .and recording the impulse at one or more receivers, aftertransmission through the neighboring formations, measurements may bemade of the amplitudes of waves received at one receiver or the ratio ofamplitudes' of waves received at two receivers. These data supply ameasure of the attenuation characteristics of the forma-4 tions. Bymeasuring such intensities or ratios of intensities at various depths ina well, a well log of the seismic wave attenuation characteristics ofthe formations is obtained.

Likewise by noting the frequency characteristicsV of waves received atdifferent depths in a well, a log of such characteristics may beobtained. In this connection, it is to be noted that even though thehammer strikes the anvil with the sarne strength at each depth and eventhough the seismic or acoustic pulse created in the anvil may besubstantially the same, the frequency characteristics of the wavesreceived by the receivers differ Widely from one depth to anotheraccording to the characteristics of the neighboring formations. Logs ofsuch frequency or attenuation characteristics for a series of wells maybe employed to correlate formations in the wells.

Although only one specic embodiment of the invention has beenillustrated and described, it is clear thatV parting from the principlesof the invention. Reference.

is therefore made to the appended claims to ascertain the scope of theinvention.

The invention claimed is:

1. In apparatus for generating seismic waves in a borehole in the earth:

an elongated tubular housing adapted to be lowered onI a cable from thesurface of the earth into the borehole, an anvil member mountedtransversely of said housing, said anvil member being adapted to becoupled to liquid inthe borehole,

an elongated hammer member movable longitudinally in said housing,

a spring normally urging said members together, and

operating means for periodically drawing said hammer member away fromsaid anvil member against the force of said spring and for periodicallyreleasing said hammer member to permit said spring to force said hammermember to strike said anvil member rapidly,

whereby a seismic impulse is periodically transmitted into the liquid inthe borehole, said operating means comprising a pair of sprockets thatare spaced `apart longitudinally in said housing,

`an endless chain looped o-ver said sprockets,

a motor arranged within said housing, and

a speed-reducing train of gears interconnecting said motor and one ofsaid sprockets for driving said chain continuously,

and wherein said hammer member is provided with a hook member movablelengthwise along one side of said chain,

said chain being provided with an outwardly extending cocking member forengaging said hook member as said cocking member passes near one of saidsprockets and for releasing said hook member as said cooking memberpasses near the other of said sprockets,

said cocking member while engaged with said hook member drawing saidhammer away from said anvil member against the force of said spring,

said spring forcing said hammer member to strike said anvil memberrapidly when said hook member is released.

2. In apparatus for generating seismic waves in a borehole in the earth:

an elongated tubular housing adapted to be lowered on a cable from thesurface of the earth into the borehole,

an anvil member mounted transversely of said housing, said anvil memberbeing adapted to be coupled to liquid in the borehole,

an elongated hammer member movable longitudinally in said housing,

a spring normally urging said members together, and

operating means for periodically drawing said hammer member away fromsaid anvil member against the force of said spring and for periodicallyreleasing said hammer member to permit said spring to force said hammermember to strike said anvil member rapidly,

whereby a seismic impulse is periodically transmitted into the liquid inthe borehole, said operating means comprising a pair of sprockets spacedapart longitudinally in said housing, an endless chain looped over saidsprockets,

a motor arranged within said housing,

and a speed-reducing train of gears interconnecting said motor with oneof said sprockets for driving said chain continuously,

and wherein said hammer member is provided with a hook member movablelengthwise along one side of said chain,

said chain being provided with a pair of uniformly spaced outwardlyextending cooking members, each cocking member engaging said hook memberas said each cocking member passes near one of said sprockets and forreleasing said hook member -as said each cocking member passes near theother of said sprockets,

said each cooking member while engaged with said hook member drawingsaid hammer member away from said anvil member against the force of saidspring,

said spring forcing said hammer member to strike said anvil memberrapidly when said hook member is released.

3. Apparatus for generating seismic waves in a bore-V hole in the earthcomprising:

an elongated tubular housing adapted to be lowered on a cable from thesurface of the earth into the bore- .16 hole, an anvil membermounted atthe bottom, end of said housing,

said anvil member being adapted to be coupled to liquid in the borehole,

an elongated hammer member movable longitudinally in said housing abovesaid anvil member,

a helical spring encircling saidhammer member normally urging saidhammer member toward said anvil member, and

operating means for periodically raising said hammer member away fromsaid anvil member against the force of said spring and for periodicallyreleasing said hammer member to permit said spring to force said hammermember to strike said anvil member rapidly,

said operating means including a pair of sprockets that are spaced apartlongitudinally in said housing. an endless chain looped over saidsprockets,

a motor arranged at the upper end of said housing,

and a speed-reducing train of gears interconnecting said motor with theupper sprocket for driving said chain continuously,

said hammer member being provided with an integral hook member movablelengthwise along one side of said chain,

said chain being provided with an outwardly extending cooking member forengaging said hook member as said cocking member passes near the lowersprocket and for releasing said hook member as said cooking memberpasses near the upper sprocket,

said cocking member while engaged with said hook member raising saidhammer member away from said anvil member against the Iforce of saidspring,

said spring forcing said hammer member to strike said anvil memberrapidly when said hook member is released,

whereby a seismic impulse is periodically transmitted into the liquid inthe borehole each time said hammer member strikes said anvil member.

4. In apparatus for determining the seismic wave transmission propertiesof formations intersected by a borehole in the earth:

an elongated testing unit adapted to be lowered on a cable from thesurface of the earth into the borehole, said testing unit including apair of elongated tubular housing members and an elongated tubularcoupling device, connecting said housing members in longitudinallyspaced apart positions.

said tubular coupling device comprising a helical spring and an elasticsleeve enclosing said spring, a body of liquid filling said tubularcoupling device,

an anvil member mounted within one of said tubular housing membersadjacent said coupling dev-ice and in contact with said body of liquid,

an elongated hammer member movable longitudinally in said one housingmember,

a helical spring encircling said elongated hammer member normally urgingand entirely lling said hammer member and said anvil member together,

means for drawing said hammer member away from said anvil member againstthe force of said spring and for releasing said hammer member to permitsaid spring to force said hammer member to strike said anvil memberrapidly,

whereby a seismic impulse is transmitted into the liquid in the boreholewhen the hammer member strikes the anvil member,

and a seismic wave receiver arranged within the other of said tubularhousing members for detecting seismic waves traveling in the surroundingformation.

5 In apparatus for determining the seismic wave transmission propertiesof formations intersected by a borehole in the earth:

an elongated testing unit adapted to be lowered on a i7 cable from thesurface of the earth into the borehole, said testing unit including aseries of at least three elongated tubular housing members, an elongatedtubular coupling device connected between successive tubular housingmembers in series and supporting said housing members in longitudinallyspaced apart position,

each of said tubular coupling devices comprising a helical spring and anelastic sleeve member enclosing each said spring, the velocity oftransmission of vibratidns in said coupling device along the lengththereof being less than about 5000 ft./sec.,

an anvil member mounted within one of said tubular housing membersadjacent a coupling device, a body of liquid in said last-mentionedcoupling device, said body of liquid being in contact with said anvilmember,

an elongated hammer member movable longitudinally in said one housingmember,

means for periodically causing said hammer member to strike said anvilmember to cause a seismic impulse to be transmitted periodically intothe liquid in the borehole, t

and a seismic wave receiver arranged within each of the other of saidtubular housing members for detecting seismic waves traveling in thesurrounding formation.

6. In apparatus for determining the seismic wave transmission propertiesof formations intersected by a borehole in the earth:

an elongated testing unit adapted to be lowered on a cable from thesurface of the earth into a borehole, said testing unit including aseries of at least three elongated tubular housing members, an elongatedtubular coupling device connected between successive tubular housingmembers in the series and supporting said housing members inlongitudinally spaced apart position,

each of said tubular coupling devices comprising a helical spring and anelastic sleeve member enclosing each said spring, the velocity oftransmission of vibrations in said coupling device along the lengththereof being less than about 5000 ft./ sec.,

an anvil member mounted within one of said tubular housing membersadjacent a coupling device, a body of liquid in said last-mentionedcoupling device, said body of liquid being in contact with said anvilmember,

an elongated hammer member movable longitudinally in said one housingmember,

a helical spring encircling said elongated hammer member normally urgingsaid hammer member and said anvil member together,

means for periodically causing said hammer member to strike said anvilmember to cause seismic impulses to be transmitted periodically into theliquid in the borehole,

a seismic wave receiver arranged within each of the other of saidtubular housing members for detecting seismic waves traveling in thesurrounding formation,

and electrical conductors connected to each of said receivers andleading upwardly through said housing members for transmitting signalsproduced by said receivers to the surface of the earth.

7. ln apparatus for determining the seismic wave transmission propertiesof formations intersected by a borehole in the earth:

an elongated testing unit adapted to be lowered on a cable from thesurface of the earth into the borehole, said testing unit including apair of elongated tubular housing members, an elongated tubular couplingdevice connected between said housing members,

said tubular coupling device comprising a helical spring and an elasticsleeve enclosing said spring,

a seismic wave generator `arranged in one of said tubular housingmembers, said seismic wave generator being adapted to transmit a seismicwave impulse into a surrounding formation,

a seismic wave receiver arranged within the other of said tubularhousing members for detecting seismic waves traveling in the surroundingformation, the time of transmission of vibrations from said anvil memberto said seismic wave receiver through said coupling device being greaterthan the time of transmission of waves from said anvil member to saidseismic wave receiver through the formation surrounding the borehole,

and electrical conductors connected to said receiver and to said seismicwave generator leading upwardly through said housing members fortransmitting signals produced by said receiver to the surface of theearth.

8. In apparatus for determining the seismic wave transmission propertiesof formations intersected by a bore hole in the earth:

an elongated testing unit adapted to be lowered on a cable from thesurface of the earth into the borehole, said testing unit including aseries of at least three elongated tubular housing members, an elongatedtubular coupling device connected between successive tubular housingmembers in the series and supporting said housing members inlongitudinally spaced apart position,

each of said tubular coupling devices comprising a helical spring and anelastic sleeve member enclosing each said spring, t

a seismic wave generator arranged in one of said tubular housingmembers, said seismic wave generator being adapted to transmit a seismicwave impulse into a surrounding formation,

a seismic wave receiver arranged within each of the other of saidtubular housing members for detecting seismic waves traveling in thesurrounding formation, the time of transmission of vibrations from saidanvil member to said seismic wave receiver through said coupling devicebeing greater than the time of transmission of waves from said anvilmember to said seismic wave receiver through the formation surroundingthe borehole,

and electrical conductors connected to said receivers and to saidseismic wave generator leading upwardly through said coupling devicesand said housing members for transmitting signals produced by'saidreceivers to the surface of the earth.

9. In apparatus for generating seismic waves in a borehole in the earth:a housing adapted to be lowered on a cable from the surface into theborehole, a pair of relatively movable members arranged in said housing,a spring normally urging said members together, means operativelycoupled to at least one of said members for periodically slowly drawingsaid members apart against the force of said spring and for releasingsaid member to permit said spring to force said members togetherrapidly, whereby a seismic impulse is periodically transmitted into theformations surrounding the borehole, and means mounted within saidhousing adjacent the path of movement of said members and responsive tomovement of said members toward one another for providing an electricalsignal indicative of the time of said seismic impulse generation.

l0. The apparatus of claim 9 wherein said housing is of elongatedtubular configuration, said pair of relatively movable memberscomprising a first anvil member extending transversely of said tubularhousing, and a second elongated hammer member extending longitudinallyin said housing, said spring comprising a strong helical compressionspring encircling said elongated hammer member throughout the largerportion of the length thereof.

ll. The apparatus of claim 9 wherein said means for providing saidelectrical signal comprises an electrical switch mounted on one of saidrelatively movable members and electrically connected to equipmentlocated at the surface of the earth, said switch being adapted to assumea first state of actuation for producing a timing signal at said earthsurface located equipment when said relatively movable members move intoengagement with one another, and being adapted to assume a non-sign-alproducing opposite state of actuation when said relatively movablemembers are remote from one another.

12. The apparatus of claim 9 wherein said means for drawing said membersapart includes an electric motor having a driving rotary member locatedwherein said housing, means within said housing operatively engageablewith at least one of said movable members and including `a driven rotarymember adapted to draw said members apart against the force of saidspring, and a speed reducing mechanism connected between said drivingmember and said driven member for rotating the latter at a lower speedthan the former and at an increased torque.

13. In apparatus for determining the"seismic wave transmissionproperties of formations intersected by a borehole in the earth: anelongated testing unit adapted to be lowered on a cable from the surfaceof the earth into the borehole, said testing unit including a series ofat least three elongated tubular housing members, an elongated couplingdevice connected between successive tubular housing mem-bers in theseriesv and supporting said housing members in longitudinally spacedapart position, each of said coupling devices including lter meanscomprising a helical spring attached at its opposing ends to an adjacentpair of said spaced housing" members for attenuating and retardng thetransmission of vibrations from one to the other of said adjacent pairof housing members, a seismic wave generator arranged in one of saidtubular housing members, said seismic wave generator being adapted totransmit a seismic wave impulse into a surrounding formation, and aseismic Wave receiver arranged within each of the other said tubularhousing members for detecting seismic Waves traveling in the surroundingformation, the time of transmission of vibrations from said anvil memberto said seismic wave receiver through said coupling device being greaterthan the time of transmission of waves from said anvil member to saidseismic Wave receiver through the formation surrounding the borehole.

14. In apparatus for generating and receiving seismic Waves in aborehole in the earth: a pair of spaced elongated tubular housingsadapted to be lowered in spaced substantially coaxial relation to oneanother on a cable from the surface of the earth into the borehole, arodshaped anvil member mountedV i-n one of said tubular housings, saidanvil member being adapted to emit vibratory energy into liquid in saidborehole when said anvil is struck, a hammer mem-ber located above saidanvil member and being movable longitudinally in said one housing, a rstspring means operatively associated with said hammer member for normallyurging said hammer member toward said anvil member, means operativelyassociated with said hammer and anvil members for raising said hammermember against the force of said spring means and for releasing saidhammer member to permit said spring means to force said hammer member tostrike said anvil member thereby to generate said seismic wave, aseismic lwave receiver in the other of said tubular housings, and meansmechanically connecting said housings to one another for simultaneouslyret-arding the passage of vibratory energy between said housingscomprising a second spring having its opposing ends spaced from oneanother and connected respectively to said pair of housings adjacent thespaced facing ends of said housmgs.

References Cited in the leof this patent UNITED STATES PATENTS 1,883,433Williams Oct. 18, 1932 2,156,052 Cooper Apr. 25, 19,39 2,233,992 WyckoffMar. 4, 1941 2,265,768 Athy et al. Dec. 9, 1941 2,681,442 Schurman June15, 1954 2,694,461 Martin Nov. 16, 1954 2,708,485 Vogel May 17, 19552,712,124 Ording f .Tune 28, 1955 2,722,282 McDonald Nov. 1 19552,728,902 White et al. Dec. 27, 1955 2,788,510 Howes Apr. 9, 19572,794,512 Martin June 4, 1957 FOREIGN PATENTS 174,354 Great Britain July19, 1923

